The invention relates to a distributed process control system for an automated plant and to a method for controlling the automated plant.
Simple automation and control engineering tasks are generally sufficient for performing process control for a plurality of plants. These tasks very often are not time-critical, having control time variables that are measured in seconds, for example water treatment in sewage treatment plants. Further general examples include pipeline management for gas, oil, and water pipeline systems, drying intermediate products in the food industry such as cooking oil drying and grain drying, and the manufacture of glass products or of flotation glass. Such plants most often have multiple physically separate, smaller automation units, so that individual tasks in the process are run in a distributed manner, and those smaller automation units may be unable to provide the kind of complex control structures and control and/or simulation strategies that can be provided by more advanced types of automation devices.
A more complex control strategy for process engineering is the model-predictive control (MPC) method, which may require significant computing capacity. It is also frequently desirable to set up simulation models, in order to be able to optimize the process using this control method. Thus computation-intensive process engineering methods or simulation models are frequently used by the more advanced control and monitoring systems of automated plants. However, to preserve the advantages of a decentralized plant concept, it is also desirable to implement such process engineering and/or simulation methods locally, close to the process itself, even if the restricted computing capacity of the automation units that are close to the process does not permit this.
The advantage of such localized process-oriented solutions is obvious, since they reduce the overall complexity and thereby make the system less prone to faults. Thus, local solutions that are connected in parallel are primarily used today to extend the automation functions of existing systems, but a significant disadvantage of these solutions is their price, the cost of the additional hardware and the service that it requires, because such solutions must be maintained locally. This maintenance of the hardware is often purely an adjustment of its parameters required by changes in the behavior of the process as the characteristic curves of the actuator hardware, such as the valves and slide switches or the pipework, change over the course of time, as deposits, wear, etc. cause general displacements in their dynamic behavior.